1. Field of the Invention
The present invention relates generally to new and useful improvements in area watering systems wherein a tower supported water pipe travels in a circular path about a central supply point, and particularly to a control valve and associated speed control device for use with the control system of such an area watering system.
2. Description of the Prior Art
The well known and widely employed irrigation devices that employ a water-turbine drive pivot require definite on-and-off modes, with no modulated condition between the definite modes. Conventionally employed is a normally closed poppet valve with a spring in series with the control linkage of the irrigating device. The addition of the spring provides the desired off-on characteristic, but also makes the valve distributing water to the driving turbine quite pressure sensitive. Changing the operating pressure in the system affects the alignment of the various units forming the irrigation system. When it is considered that the self-propelled sprinkler irrigation systems operating around a center pivot can be approximately one-quarter of a mile in length and make a complete rotation in from 24 to 60 hours, it will be appreciated that alignment of the various units forming the total length, or span, of the center pivot system is highly critical. Accordingly, the pivot must be calibrated at a given pressure and this pressure must then be maintained in order to prevent the machine from bowing. If the bow is allowed to become excessive, the pivot can walk in on itself and cause damage to the machine. In practice, however, it has been found impractical to maintain the given calibrated pressure, with the result that changes of alignment of the machine makes it impossible to use the pivot point of the system for control of part circle stop switches and end gun control. Further, a large angle error can exist between the pivot point and the end of the machine.
I am aware of the following patents that may be pertinent to the invention:
U.S. Pat. No. 3,246,848 to E. A. Bowers filed on Apr. 19, 1966
U.S. Pat. No. 3,255,968 to R. R. Stafford filed on June 14, 1966
U.S. Pat. No. 3,446,434 to F. J. Smith, Jr. et al filed on May 27, 1969